1. Field of the Invention
Embodiments of the invention relates to the field of semiconductor, and more specifically, to semiconductor fabrication.
2. Description of Related Art
Low dielectric constant (low-k) materials are used in interlayer dielectrics (ILD) in semiconductor devices to reduce propagation delay and improve device performance. As device sizes continue to shrink, the dielectric constant of the material between the metal lines should decrease to maintain the improvement. The eventual limit for the dielectric constant is k=1, which is the value for vacuum. This can be achieved by producing a void space between the metal lines, effectively creating an air gap. Air itself has a dielectric constant very close to 1. As integrated circuit (IC) technology scales, there is an increasing need to integrate low-k dielectric or even air as ILD material in order to meet the performance targets. However, the consequence is the drastic deterioration of the ILD mechanical properties. The intrinsic and extrinsic stresses become more concentrated on the metal interconnects.
Existing techniques to enhance the mechanical robustness of interconnects have a number of drawbacks. One technique is to increase the via density. However, the electrical nature of the conducting vias severely limit the via density or device layout due to the potential shorting of adjacent circuitry. Another technique is to integrate strong dielectric materials, usually with higher k value, at the via level as discrete dielectric lines or as mechanical pillars. This technique increases the complexity of the fabrication process and introduces additional dielectric materials. In air gap techniques, new materials are necessary to enable the process.